Add missing `?Sized` bounds to `io::Write` parameters

Since we are no longer relying on the blanket `io::Write` impl for
`&mut io::Write`, we should now ensure that we do not require
`Sized` for our `io::Write` bounds, as its unnecessarily
restrictive and can no longer be worked around by simply adding an
`&mut`.

bitcoin/src/crypto/key.rs

@@ -68,7 +68,7 @@ impl PublicKey {
     }
 
     /// Write the public key into a writer
-    pub fn write_into<W: io::Write>(&self, writer: &mut W) -> Result<(), io::Error> {
+    pub fn write_into<W: io::Write + ?Sized>(&self, writer: &mut W) -> Result<(), io::Error> {
         self.with_serialized(|bytes| writer.write_all(bytes))
     }
 

bitcoin/src/crypto/sighash.rs

@@ -673,7 +673,7 @@ impl<R: Borrow<Transaction>> SighashCache<R> {
 
     /// Encodes the BIP341 signing data for any flag type into a given object implementing a
     /// [`io::Write`] trait.
-    pub fn taproot_encode_signing_data_to<Write: io::Write, T: Borrow<TxOut>>(
+    pub fn taproot_encode_signing_data_to<Write: io::Write + ?Sized, T: Borrow<TxOut>>(
         &mut self,
         writer: &mut Write,
         input_index: usize,
@@ -860,7 +860,7 @@ impl<R: Borrow<Transaction>> SighashCache<R> {
     /// `script_code` is dependent on the type of the spend transaction. For p2wpkh use
     /// [`Script::p2wpkh_script_code`], for p2wsh just pass in the witness script. (Also see
     /// [`Self::p2wpkh_signature_hash`] and [`SighashCache::p2wsh_signature_hash`].)
-    pub fn segwit_v0_encode_signing_data_to<Write: io::Write>(
+    pub fn segwit_v0_encode_signing_data_to<Write: io::Write + ?Sized>(
         &mut self,
         writer: &mut Write,
         input_index: usize,
@@ -984,7 +984,7 @@ impl<R: Borrow<Transaction>> SighashCache<R> {
     ///
     /// This function can't handle the SIGHASH_SINGLE bug internally, so it returns [`EncodeSigningDataResult`]
     /// that must be handled by the caller (see [`EncodeSigningDataResult::is_sighash_single_bug`]).
-    pub fn legacy_encode_signing_data_to<Write: io::Write, U: Into<u32>>(
+    pub fn legacy_encode_signing_data_to<Write: io::Write + ?Sized, U: Into<u32>>(
         &self,
         writer: &mut Write,
         input_index: usize,
@@ -1011,7 +1011,7 @@ impl<R: Borrow<Transaction>> SighashCache<R> {
             return EncodeSigningDataResult::SighashSingleBug;
         }
 
-        fn encode_signing_data_to_inner<Write: io::Write>(
+        fn encode_signing_data_to_inner<Write: io::Write + ?Sized>(
             self_: &Transaction,
             writer: &mut Write,
             input_index: usize,

bitcoin/src/taproot.rs

@@ -1109,7 +1109,7 @@ impl TaprootMerkleBranch {
     /// # Returns
     ///
     /// The number of bytes written to the writer.
-    pub fn encode<Write: io::Write>(&self, writer: &mut Write) -> io::Result<usize> {
+    pub fn encode<Write: io::Write + ?Sized>(&self, writer: &mut Write) -> io::Result<usize> {
         for hash in self.0.iter() {
             writer.write_all(hash.as_ref())?;
         }
@@ -1237,7 +1237,7 @@ impl ControlBlock {
     /// # Returns
     ///
     /// The number of bytes written to the writer.
-    pub fn encode<Write: io::Write>(&self, writer: &mut Write) -> io::Result<usize> {
+    pub fn encode<Write: io::Write + ?Sized>(&self, writer: &mut Write) -> io::Result<usize> {
         let first_byte: u8 =
             i32::from(self.output_key_parity) as u8 | self.leaf_version.to_consensus();
         writer.write_all(&[first_byte])?;